Pulse sequence detector
The resistor divider connected between Ql and Q2 supplies IH to Ql after input A triggers it. It also prevents input from triggering Q2 until Ql conducts....
Gated pulse descrambler
This circuit consists of an amplifier and video detector with a second subcarrier detector for synch recovery purposes. A pulse-former circuit modulates the gai...
Attendance counter
The display shows each increment. By using mode 2, external debouncing of the gate switch is unnecessary, provided the switch bounce is less than 35ms. The 3 V ...
Binary counter
Stages are triggered by the positive going edge. The scs is turned on at the cathode gate; turned off at the anode gate. The anode-to-cathode IN4009 suppresses ...
20 Khz ring counter
The shift pulse turns off the conducting scs by reverse biasing the cathode gate. The charge stored on the coupling capacitor then triggers the next stage. An e...
8-Digit up-down counter
This circuit shows how to cascade counters and retain correct leading zero blanking. The NAND gate detects whether a digit is active since one of the two segmen...
Mux-Demux system
A number of signals may be sent between two points simultaneously by making a slight modification in the receiver circuit. ...
8-bit bus interface
With this double latch technique, valid data will be latched to the DAC until updated with the E2 pulse....
Frequency comparator circuit
Input 1 is used as a gating period, during which a single rising edge on input 2 will cause a logic 1 output-any other number, indicating non-identical frequenc...
Up-down-counter
The discrete-gate up/down-counter design has the unusual property of freezing, or saturating, when it reaches its lowest count in the down-count mode or its hi...
Electronic lock using the 4022 octal counter
The heart of the lock is the 40022 octal counter. When first powered C2 is charged via R5 so the reset input of the counter is kept high. That causes output Q t...
Digital Gates
You're simulating a circuit, it requires several digital gates, but you don't have a mixed-mode simulator. What to do? One solution involves creating simplified...
Hi-Low Logic Digital tester
This tester, the logic level digital signals indicate on a 7-segment display. The display shows an H as the input signal is high. When the signal is low, the di...
Digital counter circuit
With this counter you can count laps for example (in conjunction with the Simple light trap ). The circuit uses two TTL ICs 74LSxx the series. The left IC is a ...
Logic level relay controller
The schematic below illustrates 4 methods of controlling a relay with a digital logic signal. Figure (A) can probably be used in most cases where the relay coil...
Bistable Flip Flop with relay
Here are two examples of bistable flip flops which can be toggled between states with a single push button. When the button is pressed, the capacitor connected ...
Set reset flip-flop circuit
This is an example of a set/reset flip flop using discrete components. When power is applied, only one of the transistors will conduct causing the other to rema...
CMOS Toggle Flip Flop Switch
The circuit below uses a CMOS dual D flip flop (CD4013) to toggle a relay or other load with a momentary push button. Several push buttons can be wired in paral...
Digital Electronic Lock schematic
The digital lock shown below uses 4 common logic ICs to allow controlling a relay by entering a 4 digit number on a keypad. The first 4 outputs from the CD4017 ...
Digital Clock with Solar Regulator
The basic clock circuit (top schematic below) is similar to the binary clock (on another page) and uses 7 ICs to produce the 20 digital bits for 12 hour time, p...